1. Field of the Invention
The present invention relates generally to semiconductor technology and, more particularly, to a method and apparatus for manufacturing metal-insulator-metal capacitors using atomic layer deposition.
2. Background of the Related Art
In the manufacture of integrated circuits, many methods are known for depositing and forming various layers on a substrate. Chemical vapor deposition (CVD) and its variant processes are utilized to deposit thin films of uniform and, often times conformal coatings over high-aspect and uneven features present on a wafer. However, as device geometries shrink and component densities increase on a wafer, new processes are needed to deposit ultrathin film layers on a wafer. The standard CVD techniques have difficulty meeting the uniformity and conformity requirements for much thinner films.
One variant of CVD to deposit thinner layers is a process known as atomic layer deposition (ALD). ALD has its roots originally in atomic layer epitaxy, which is described in U.S. Pat. Nos. 4,058,430 and 4,413,022 and in an article titled xe2x80x9cAtomic Layer Epitaxyxe2x80x9d by Goodman et al., J. Appl. Phys. 60(3), Aug. 1, 1986; pp. R65-R80. Generally, ALD is a process wherein conventional CVD processes are divided into single-monolayer depositions, wherein each separate deposition step theoretically reaches saturation at a single molecular or atomic monolayer thickness and, then, self-terminates.
The deposition is an outcome of chemical reactions between reactive molecular precursors and the substrate (either the base substrate or layers formed on the base substrate). The elements comprising the film are delivered as molecular precursors. The desired net reaction is to deposit a pure film and eliminate xe2x80x9cextraxe2x80x9d atoms (molecules) that comprise the molecular precursors (ligands). In a standard CVD process, the precursors are fed simultaneously into the reactor. In an ALD process, the precursors are introduced into the reactor separately, typically by alternating the flow, so that only one precursor at a time is introduced into the reactor. For example, the first precursor could be a metal precursor containing a metal element M, which is bonded to an atomic or molecular ligand L to form a volatile molecule MLx. The metal precursor reacts with the substrate to deposit a monolayer of the metal M with its passivating ligand. The chamber is purged and, then, followed by an introduction of a second precursor. The second precursor is introduced to restore the surface reactivity towards the metal precursor for depositing the next layer of metal. Thus, ALD allows for single layer growth per cycle, so that much tighter thickness controls can be exercised over standard CVD process. The tighter controls allow for ultrathin films to be grown.
CVD is a typical process for use in forming metal-insulator-metal (MIM) capacitors. MIM capacitors are implemented by a sequence that includes bottom metal deposition, patterning, dielectric deposition, top metal deposition and patterning. MIM capacitors are utilized in a variety of devices, including memory devices (such as dynamic random-access-memory, or DRAM). The general use of MIM capacitors in integrated circuits and RF circuits is known in the art.
Although currently manufactured MIM capacitors use CVD technology, none are known to have been fabricated by ALD. Since ALD has the ability to deposit continuous ultrathin films of conductive, semiconductive or insulating (dielectric) material on complicated geometries, yet retain good uniformity and conformity, ALD is attractive for fabricating MIM capacitors. The present invention is directed to providing the integration of ALD for the manufacture of MIM capacitors.
A method and apparatus for depositing a first conductive layer by atomic layer deposition and depositing a sacrificial layer above the first conductive layer also by atomic layer deposition without exposing the first conductive layer to oxidation. A defined structure is then formed by removing portions of the first conductive and sacrificial layers. Next, the sacrificial layer is removed to expose the underlying first conductive layer without exposing the first conductive layer to oxidation. A dielectric layer is next deposited over the exposed first conductive layer by atomic layer deposition. To form a metal-insulator-metal (MIM) capacitor, the stack is completed by depositing a top conductive layer.